Fix embind failing in workers when STACK_OVERFLOW_CHECK is enabled (#12366)

Initialization of embind must be done at the proper time, so that
the stack check information is already set up and can work
properly.

Fixes #12356.

Author: tklajnscek

src/library_pthread.js

@@ -94,10 +94,6 @@ var LibraryPThread = {
     },
     initWorker: function() {
       PThread.initShared();
-#if EMBIND
-      // Embind must initialize itself on all threads, as it generates support JS.
-      Module['___embind_register_native_and_builtin_types']();
-#endif // EMBIND
 #if MODULARIZE
       // The promise resolve function typically gets called as part of the execution
       // of the Module `run`. The workers/pthreads don't execute `run` here, they

src/worker.js

@@ -12,6 +12,9 @@
 var threadInfoStruct = 0; // Info area for this thread in Emscripten HEAP (shared). If zero, this worker is not currently hosting an executing pthread.
 var selfThreadId = 0; // The ID of this thread. 0 if not hosting a pthread.
 var parentThreadId = 0; // The ID of the parent pthread that launched this thread.
+#if EMBIND
+var initializedJS = false; // Guard variable for one-time init of the JS state (currently only embind types registration)
+#endif
 
 var Module = {};
 
@@ -178,6 +181,15 @@ this.onmessage = function(e) {
       Module['PThread'].receiveObjectTransfer(e.data);
       Module['PThread'].setThreadStatus(Module['_pthread_self'](), 1/*EM_THREAD_STATUS_RUNNING*/);
 
+#if EMBIND
+      // Embind must initialize itself on all threads, as it generates support JS.
+      // We only do this once per worker since they get reused
+      if (!initializedJS) {
+        Module['___embind_register_native_and_builtin_types']();
+        initializedJS = true;
+      }
+#endif // EMBIND
+
       try {
         // pthread entry points are always of signature 'void *ThreadMain(void *arg)'
         // Native codebases sometimes spawn threads with other thread entry point signatures,

tests/test_core.py

@@ -8176,6 +8176,11 @@ def test():
     self.emcc_args += ['-DPOOL']
     test()
 
+    print('with embind and stack overflow checks (see #12356)')
+    self.set_setting('STACK_OVERFLOW_CHECK', 2)
+    self.emcc_args += ['--bind']
+    test()
+
   @node_pthreads
   def test_pthread_exceptions(self):
     self.set_setting('PTHREAD_POOL_SIZE', '2')